1. Field of the Invention
The present invention generally relates to a torque converter disposed between an engine and a transmission. More specifically, the present invention relates to torque converter lockup control technology that controls the lockup capacity of the torque converter during a coast-running condition, i.e., when the accelerator pedal is released.
2. Background Information
A torque converter is typically disposed between an engine and an automatic transmission including a continuously variable transmission. The torque converter has a torque increasing action and a torque fluctuation absorbing function. However, a rotational difference sometimes arises between the rotation of the pump impeller, which is an engine input element, and the turbine runner, which is a transmission output element. This rotational difference is accompanied by a slip causing the transmission efficiency to deteriorate. Thus, conventionally a lockup mechanism has been disposed which eliminates slip by mechanically locking the input/output elements when the torque increasing action and the torque fluctuation absorbing function are unnecessary. The lockup of the input/output elements is conducted by a lockup clutch. The lockup clutch control device controls the lockup capacity, which is the clutch lockup pressure, whereby it is possible for the lockup clutch to turn the lockup state into a complete lock state or a slip-lock state.
Recently, vehicles have been developed that are provided with a fuel cutting function that stops the injection of fuel to the combustion chamber of the engine in order to prevent useless fuel consumption during a vehicle coast-running condition at the time of acceleration pedal release when the driver releases his/her foot from the acceleration pedal. It is common to set a predetermined cut-in delay time (start delay time) for performing the fuel cutting function such that fuel cutting is executed after all of the in-cylinder air present from the completely closed throttle valve to the combustion chamber reaches the engine after the acceleration pedal release. During fuel cutting execution, it is necessary to prevent the engine from stalling by mechanically coupling the engine to tire rotational elements that rotate with the tires during coast-running. Specifically, lockup resulting from the slip lockup is conducted to prevent the engine rotation from becoming zero.
On example of a conventional lockup control device is disclosed in Japanese Laid Open Patent Publication No. 2001-208193. In this publication, it is disclosed to prevent the engine from stalling by controlling the lockup capacity on the basis of the vehicle running condition when a lockup resulting from slip lockup is conducted. The lockup capacity control device disclosed in Japanese Laid Open Patent Publication No. 2001-208193 controls the lockup capacity in accordance with the state of the operational load of the in-vehicle air conditioner. Namely, the lockup capacity is increased when the operational load of the in-vehicle air conditioner is high, whereby the reverse drive torque (coast torque) transmitted from the wheels to the engine is reliably transmitted to the engine to maintain the engine rotation. The lockup capacity is reduced when the operational load of the in-vehicle air conditioner is low, whereby quick release of the lockup (slip-lock state) is enabled and engine stall is prevented.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved torque converter. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.